Conventionally, rotary cutting dies have been manufactured by drawing a figure on a curved surface plywood sheet having a thickness of 13 mm (0.5 in.) or 16 mm, and cutting the plywood by use of a manually operated jigsaw. The groove width is generally 4 point (1.42 mm).
Recently, a method which uses a carbon-dioxide laser and a numerical controller for cutting a curved surface plywood has been proposed. For example, Utility Model No. 3015518 has proposed it. A curved blade is inserted into the cut groove to provide a finished rotary cutting die.
Recently, Gerber Scientific Products, Inc. has proposed a method for cutting a flat plate die that uses a router instead of a costly laser cutting machine. The drill bit for use with the router is shown in U.S. Design Pat. No. 447495. FIG. 1 is a sectional view of a flat plate cutting die produced with a router manufactured by Gerber Scientific Products, Inc. To produce such a flat plate cutting die, two plywood sheets 9 mm thick are cut in mirror image. Then, the back surface of the upper plywood sheet 3 and that of the lower plywood sheet 2 are bonded to each other. The drill bit has such a geometrical feature that, if it is for 2-point-wide (0.72-mm-wide) groove cutting, for example, the portion in the range of 2.5 mm from the tip is cylindrical, having a diameter of 0.72 mm. The portion beyond the range of 2.5 mm from the tip is funneled. This is because, if a diameter of 0.72 mm were provided for the drill bit over the entire length of 9 mm from the tip, the strength of the drill bit could not be maintained, resulting in breakage. The flat plate cutting die is made of a 18-mm- or 16-mm-thick plywood, however, if 9- or 8-mm-thick plywood sheets cut with the drill bit are bonded to each other, an 18-mm- or 16-mm-thick plywood sheet can be produced, and a 2.5-mm-deep straight groove for holding a 0.72-mm-thick blade can be created in both front and back surfaces of the bonded plywood. On the other hand, the curved surface plywood for rotary cutting die is generally 13 mm thick (½ in.). The thickness as large as 13 mm cannot be cut with a 4-point drill bit at a time. Thus, the thickness of 13 mm must be divided. But, any curved surface plywood cannot be turned inside out for bonding it to a curved surface plywood which is not turned inside out. Therefore, this turning-inside-out technique cannot be used with a drill bit having a 1.4-mm diameter.
In USA, the rotary cutting die plywood generally has a thickness of 13 mm (½ in.). In Japan, a thickness of 16 mm is also used. The diameter of the rotary cutting machine cylinder is generally 487 mm or 360 mm in USA. In Japan, 10 or more different diameters are used. The thickness of the rotary cutting blade (steel rule knife) used in USA is generally 4 point (1.4 mm). This statement is for the soft anvil method. When a rotary cutting machine cuts by the soft anvil method, the rotating blade is formed as a serrated rule, and cuts into a urethane cylinder which is also rotated for cutting a corrugated cardboard. In Japan, the hard anvil method is also used. The blade is not serrated as is the case with that for the flat plate die. The mating cylinder is made of a steel plate, and the blade will not cut into it. In hard anvil cutting, the rotary cutting die uses a 1.0-mm thick (3 point) blade.